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Most efficient method to limit voltage to a motor controller.

Most efficient method to limit voltage to a motor controller.

Most efficient method to limit voltage to a motor controller.

A switcher can work. Do not try zeners or linear regulators, they will get very hot (around 150 W to burn). The best way is to use three six volt batteries or one 12 V and one 6 V.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Most efficient method to limit voltage to a motor controller.

>>>two 12v batteries wired in a series parallel arrangment to18volts<<<

Huh?  From that combo, you can get 12V in parallel, or 24V in series.
To get 18V, you need three 6V batteries in series.

Or, as Gunnar said, a switching DC/DC converter.  But then, what are you going to do with 18V?  Just turn it loose on the wheel motors?   And do wheelies?

If the bridges can switch 24V, that's what I would do, turn them on and off rapidly, using the duty cycle to control the speed of the wheel motors.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Most efficient method to limit voltage to a motor controller.

Sounds like he wants to slow it down; says it "was 24 v" and now he wants to limit it to 18 volts.  Agree, the easiest way with DC is to start with 18 volts or PWM the switches.

RE: Most efficient method to limit voltage to a motor controller.

(OP)
I purchased some "high power" motor controllers from the Pololu site for robotics. I meant to purchase the ones that were rated 24v. The ones I have are rated at 18v. I am going to control speed and torque of the motors via a PWM signal from the motor controllers I just need to step the voltage down to 18v supply to the controllers. I would have trouble going to a 3 x 6v battery arrangment due to the mounting system for the batteries. It may be easier to return the 18v units and pick up the 24v ones. I just thought if I could efficiently reduce the votlage then maybe I could extend the runtime by thoretically having some voltage in reserve.  

RE: Most efficient method to limit voltage to a motor controller.

Good decision to buy the right controllers. You gain nothing but problems if you don't.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Most efficient method to limit voltage to a motor controller.

Okay, you can put a switching regulator in there, but at that power level it won't be cheap, and your first design probably won't work right, at which point you'll get to buy new motor controllers anyway.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Most efficient method to limit voltage to a motor controller.

(OP)
Guys I appreciate all of the feedback. Question, If I connect a 12v and 6v in a series parallel arrangment will I get 18v? I have never tried to mix the voltages.

 

RE: Most efficient method to limit voltage to a motor controller.

What do you mean by series parallel arrangement?

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Most efficient method to limit voltage to a motor controller.

You won't get any "voltage in reserve" by running 24V batteries with something reducing the controller voltage to 18V. The voltage only really starts to collapse when the batteries are dead, and at that point they are dead and are not capable of sourcing more power until they are "more dead".

2 batteries can't be hooked in both series and parallel at the same time. You have to pick one, either series or parallel.

You are better off just returning the controllers and getting the correct voltage controllers. You'll will not find it cost effective to build or buy a device to reduce the battery voltage to 18V.

There is no reason you can't put a 12V and 6V battery in series. Make sure the cells have the same ratings if you're planning on using a 18V charger.
 

RE: Most efficient method to limit voltage to a motor controller.

(OP)
I was taught that if you hook ground to the chassis on 1 battery then the positive lead to the negative lead on the other battery you will get the battery voltage x 2 between the positive of one battery and the chassis or ground of the other. Thus is a series parallel arrangment. Every piece of heavy equipment that uses 24 volts is wired this way.    

RE: Most efficient method to limit voltage to a motor controller.

Quote:

Thus is a series parallel arrangment.
Not really.
Some equipment has a 12 volt system, 12 Volt alternator, 12 Volt lights, 12 Volt accessories, etc. But the starter is 24 volts.
A special solenoid type switch disconnects one battery and reconnects it in series to provide 24 Volts to the starter only. This is the series parallel switch. The other battery remains connected to and supplies 12 Volts to the rest of the system. When you turn off the starter, the series parallel switch returns the second battery connections to parallel so that it may be recharged by the 12 Volt alternator. Now if you have an old Kenworth with four six volt batteries (was looking at one the other day) then you have a true series parallel connection when on 12 Volts.
Each set of two six volt batteries is in series to provide 12 Volts and the series parallel switch reconnects all four batteries in series for starting.

Quote:

Every piece of heavy equipment that uses 24 volts is wired this way.
Not really.
Alternately, there are equipment systems that are completely 24 Volts. 24 Volt alternators, 24 Volt starters, 24 Volt lights and, most importantly for the operator who was told that cell phones were banned on site, a 24 Volt cigarette lighter. 24 Volts to the charger will fry a cell phone right now.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Most efficient method to limit voltage to a motor controller.

(OP)
You are right there are some systems that use 24v to start and 12v to run. I meant when a piece of equipment is 24v start and 24v run then they are wired in series parallel. Are you saying that two batteries wired positive to negative with the vehicle connections on the ends--the other positive and negative-- then they are only parallel? And when you have say 4 batteries that are six volts each pair in series and the the two pair wired in parallel then that is series parallel?  

RE: Most efficient method to limit voltage to a motor controller.

Hey heavy, are you here to start a flame war?

Or are you, as a structural guy, trying to teach us seasoned and knowledgeble engineers about electricity and terminology?

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Most efficient method to limit voltage to a motor controller.

(OP)
no i was actually just trying to make sure i had my terminology correct. I started off as a technician in the Marine Corp and then worked in the crane industry as a service technician before I started into rigging engineering which is basically structural applications of statics. I have a pretty good handle on practical applications of troubleshooting electrical systems mainly PLC systems.

I am NOT and electrical engineer which is why came to this site to ask questions from the experts. I just wanted to make sure I understood the difference.

I attached a sketch with my undrstanding of the two different systems. Maybe it will help with my explanation.

RE: Most efficient method to limit voltage to a motor controller.

Back on subject, in this case two wrongs probably equal more expensive.  Good choice to return the 18 volt controllers.

RE: Most efficient method to limit voltage to a motor controller.

Two 12V batteries wired to produce 24V is a SERIES connection. It is NOT parallel or series/parallel.

A system with 2 batteries that switches between 12V and 24V is not connected series/parallel either. It switches between a series connection and a parallel connection. It is never connected in both series and parallel at the same time.

You need to look it up series and parallel connections if you don't understand. We're not explaining such basic entry level topics here.

RE: Most efficient method to limit voltage to a motor controller.

(OP)
I would like to thank you guys for your rapid responses and for all of the help. I believe I will return them and get the ones rated for the proper voltage. I just didnt want to go through the hassle of mailing them back etc. only to find out that with a couple of components I could have used them.

Thanks again, this forum is a great resource.

I am still interested in outcome of the series-parallel debate.....I actually taught electrical troublshooting for two years for a major crane company, Demag Mobile Cranes. Lucky for my students it was focused on practial troublshooting and not theoretical electrical fundamentals or terminology. I was basically how to read european E-Lan schematics and how to use a multi meter and milliamp driver to test and elimiate sensors etc.  

RE: Most efficient method to limit voltage to a motor controller.

The top drawing you posted shows two 12v batteries in "series".  The bottom drawing you posted shows two pair of batteries in parallel, but the wire connecting the two pairs should run from positive to negative (instead of positive to positive) to put the pairs in series. I have attached a drawing...

RE: Most efficient method to limit voltage to a motor controller.

OK heavy, I was a bit harsh on you. But when complete ignorants try to tell the experts about basic things, I get mean. No bite, though. Just bark.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Most efficient method to limit voltage to a motor controller.

Many 12:24 volt systems use two 12 volt batteries. Parallel for 12 Volt operation and series for 24 Volt starting. A switch called a series parallel switch changes the connection from parallel to series. The only true series parallel connection of the batteries is when four 6 Volt batteries are used and then only when configured for 12 Volt operation and charging,
Regarding your sketch;
1/ The top sketch is a series connection.
2/ The 12 Volt labels on the second sketch should be 6 Volts.
3/ The 24 Volt label should be 12 Volts.
4/ The series label should be parallel.
5/ The parallel label should be series.
6/ The connection as you have shown it is not the connection used in trucks and will not develop 24 Volts.
Hence the frustration of some of the gurus here.
Please do a little Googling on series parallel systems.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Most efficient method to limit voltage to a motor controller.

Quote:

I am still interested in outcome of the series-parallel debate

What debate? Your description of a series connection as being series/parallel is wrong.

Your drawing is also all wrong. The top picture is a series connection. The bottom arrangement is a complete mess. It basically shows the 2 right batteries connected in parallel to provide 6V output. The left 2 are also connected in parallel but the negative terminals are not connected to the "outside world" and those batteries won't be used for anything.

http://lmgtfy.com/?q=series+parallel
 

RE: Most efficient method to limit voltage to a motor controller.

I have seen 4 batteries connected in a so called "series-parallel" arrangement.  

This consisted of 2 pairs of 6 volt batteries, each pair connected in series for 12 volts and then the two series groups connected in parallel to supply 12 volts to the load (starter).

This was in 1970's heavy trucks.  On some the 4 batteries were all in one battery box, on the others, there was one pair on each side of the truck.
 

RE: Most efficient method to limit voltage to a motor controller.

The battery experts are obviously in structural and agriculture - and their expertise stems from 1970  smile

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Most efficient method to limit voltage to a motor controller.

Gunnar, that must be a typo. You mean 1097. smile
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Most efficient method to limit voltage to a motor controller.

(OP)
http://www.accessconnect.com/images/batteries_series_parallel.jpg

Apparently my terminology was not accurate, the link above is a diagram from google as one of you helpful EEs suggested. This is what I was taught in school to be a series parallel circuit.

I don't mind being wrong but I don't like to be ridiculed for asking a question. I didn't realize that electrical engineers were above a simple discussion.

I am quite sure none of you would be so bold. I would love to sit face to face and have this same discussion with any one if you.

To those of you who are more interested in helping than getting offended because someone questioned your written word, I appreciate your help.

 

RE: Most efficient method to limit voltage to a motor controller.

What about just accepting that you have things to learn? It is your stubborn "Still, I am right" attitude that irritates more than your lack of knowledge.

What you show is a parallel-series arrangement - no doubt. But it is not possible to "parallel-series" connect two batteries as you suggested.

Just leave it there and buy controllers that work with the supply voltage you have got.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Most efficient method to limit voltage to a motor controller.

That is indeed a series parallel circuit, but it is not equivalent to the series circuit (comprising two, not four, batteries) that you erroneously characterized as series parallel.  

To sort of answer that question, from where the discussion went off the rails, yes you can connect a 12V battery and a 6V battery in series to get 18 volts.  It works better if the cells are all similar, i.e. same A-H rating and same chemistry, so it would be better to connect 3 identical 6V batteries in series to get an 18V battery.  If you do that, you will need an 18V charger.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Most efficient method to limit voltage to a motor controller.

Yes that is a series parallel arrangement.  Now google series parallel starting circuits.
When engine people are talking about a series parallel system, they are referring to the switching arrangement via a "Series-Parallel Switch" that provides 24 Volts for starting. Two issues that confuse each other.
1/ Connecting two 6 Volt batteries in series for the equivalent of a 12 Volt battery.
2/ Connecting two 12 Volt batteries in series to provide 24 Volts for starting.
At a time when money was tighter and batteries often failed because one cell had gone open prematurely, it was cheaper to change out a 6 Volt battery than a 12 Volt battery. Also large 6 Volt batteries were readily available in most areas. Large 12 Volt batteries were not nearly as common when this system was originally supplied.
Yes, I know, 8D batteries were probably available but these would be expensive and heavy overkill, especially when the battery had to be replaced because of one failed cell.
Back in the 40's when these systems came into use, 12 Volt batteries were found to be inadequate for the dependable starting of large diesel engines. Given the rougher roads, light bulb technology was not adequate to supply filaments that were dependable at 24 Volts. (At a given wattage a 12 volt filament is much heavier and stronger than a 24 Volt filament.)
To address these issues the series parallel switch was developed to provide 24 Volt starting and the use of 12 Volt lamps and accessories.
At this time, (1940's most North American cars used 6 Volt batteries and 6 volt battaries were available almost anywhere. Hence the use of 2 6 Volt batteries in place of one 12 Volt battery.
Last week I was asked to check an old 4x6Volt system to see if the batteries were connected properly. Yes Gunnar, the truck is in agricultural service. grin

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Most efficient method to limit voltage to a motor controller.

(OP)
I purchased to correct controllers as suggested by someone early on.

I do realize that I have a lot to learn which is awesome because learning is my favorite part about the engineering profession. I learn something on every project that I take on.

The reason I posted the drawing is that I wanted to make sure I was aligning my understanding of the terminology with a proper drawing.

Skagsurra or what ever you name is, the comment about all of the battery experts being in the structural or ag disciplines is what pissed me off, just because someone asks a question or try's to point out their point of view doesn't mean that they consider themselves experts. I pointed these examples out not as arguments or to challenge your knowledge but in hopes that you or someone would maybe explain the error that I was making to me. Some of the members here did exactly that such a waross and a few if the other members.

Anyway my problem has been solved so again I say thank you.  

RE: Most efficient method to limit voltage to a motor controller.

Hmm.. My handle can easily be copied and pasted in case you have a problem with it.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Most efficient method to limit voltage to a motor controller.

As an engineer, you should have the capability of performing a simple task such as Google search so you understand the terminology, instead of posting back multiple times about what you were taught or what you think you understood.
 

RE: Most efficient method to limit voltage to a motor controller.

Series parallel terminology. Simple but:
Series parallel may be passive or active (for want of better terms).  Four 6 Volt batteries connected for 12 Volts would be a passive series parallel application. This is the application that electrical circuit people may be most familiar with.
In automotive applications a switch (a series parallel switch) that connects 12 Volt batteries in either series or parallel would be an active series parallel application. This is the series parallel application that automotive people may be most familiar with.
Although not as common now as in years past, some truck manufacturers used four 6 Volt batteries in a passive series parallel connection for 12 Volt service and reconnected them all in series with an active series parallel switch for 24 Volt starting.

Bill
--------------------
"Why not the best?"
Jimmy Carter

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